1. Field of the Invention
The present invention relates an ignition timing control apparatus for an internal combustion engine (hereinafter, an engine) capable of detecting a level of knocking, and controlling an ignition timing corresponding to a result of the detection.
2. Discussion of Background
As a conventional ignition timing control apparatus for an engine, there is one disclosed, in Japanese Unexamined Patent Publication No. 58055/1987. This apparatus detects a crank angle (.theta..sub.pmax) in which a combustion pressure is maximized, from an inner cylinder pressure (pressure inside of cylinder) of the engine, and detects knocking by the comparison between .theta..sub.pmax and a knocking limit value (.theta..sub.k) of a knocking generation limit which corresponds with a running condition of the engine predetermined by a revolution number and a load of the engine. When .theta..sub.pmax .gtoreq..theta..sub.k, a judgment is made wherein the knocking is not generated, and the ignition timing is advanced. When .theta..sub.pmax &lt;.theta..sub.k, a judgment is made wherein the knocking is not generated, and the ignition timing is retarded for the control of knocking.
Since the conventional ignition timing control device of an engine is composed as mentioned above, a crank angle wherein the combustion pressure is maximized, is detected. However, this value does not directly represent the output of the engine. Therefore, even if the engine is controlled with the ignition timing determined by this value, the maximum output of the engine may not be attained.
Moreover, the predetermined knocking limit value (.theta..sub.k) of the knocking generation limit may be deviated from the optimum value due to the variation of the engine or the timewise change of the engine. This causes the lowering of the detection accuracy of knocking or the delay of the control response. In such case the knocking may not be controlled, or the responsiveness of the control may be delayed.